Meteor travelling at 18 kilometres per second released about 33 times the energy of the Hiroshima atomic bomb

A meteor that exploded in the sky above Russia's Ural Mountains was the largest since the Tunguska blast in Siberia in 1908 and released about 33 times the energy of the atomic bomb that destroyed Hiroshima.

Before hitting the Earth's atmosphere on Friday, the object was about 17 metres in size and had a mass of about 10,000 tonnes, NASA said. Russian scientists offered vastly different statistics, saying the meteor weighed about 10 tonnes.

"We would expect an event of this magnitude to occur once every 100 years on average," Paul Chodas of NASA's Near-Earth Object Program Office said. The Chelyabinsk meteor released 500 kilotons of energy when it disintegrated above the city of Chelyabinsk about 9.20am local time, according to NASA. The atomic bomb dropped on Hiroshima in 1945 was 12-15 kilotons.

Unrelated to asteroid 2012 DA14, which flew past by Earth safely, the Chelyabinsk meteor hit the atmosphere at a speed of 18 kilometres per second (40,000 miles per hour) and took 32.5 seconds to break apart 15 kilometres to 25 kilometres above the Russian city, according to NASA.

Shock wave

The shock wave from the meteor blew out windows in 3700 buildings in and around Chelyabinsk, the regional government said in a statement. About 1150 people sought medical attention, of whom more than 50 were admitted to hospital, the Russian Health Ministry said.

Burning streaks lit up the sky in videos that were caught by drivers on dashboard cameras, broadcast on Russian television and posted on YouTube. The force destroyed a warehouse wall at the OAO Chelyabinsk Zinc Plant and disrupted service from Russia's second-biggest mobile operator, OAO MegaFon.

The Tunguska event, which was the most powerful natural explosion in the modern era, levelled about 2100 square kilometres of forest in Siberia, while leaving no crater, according to NASA.

The asteroid that scientists say ploughed into Earth about 66 million years ago, wiping out the dinosaurs, may have been about 10 kilometres in diameter.

A United Nations team met in Vienna last week to come up with recommendations on how best to track, and someday deflect or destroy, orbiting space rocks.